Abstract Alternaria cichorii was recorded for the first time in Brazil causing leaf spots on endive (Cichorium endivia) in 2003 based on material collected at Catalão, state of Goiás, in 2001. In 2005, A. cichorii was found causing severe leaf-spotting in an escarole (C. endivia) plantation in Viçosa, state of Minas Gerais and shortly afterwards also in Viçosa, but at a different location, in the weed hosts common sowthistle (Sonchus oleraceus) and spiny sowthistle (Sonchus asper). A description of A. cichorii based on specimens collected in Viçosa is provided herein. The natural occurrence of A. cichorii on weed hosts in Viçosa indicates that it has already become naturalized in Brazil surviving on non-cultivated composites, complicating disease management. Pathogenicity tests, complementary to those already published, were performed to better elucidate the range of potential alternative hosts in the Asteraceae of this fungus. This involved inoculation of one isolate of A. cichorii obtained from cichory and one obtained from common sowthistle on selected species and cultivars of 10 tribes in the Asteraceae, but concentrated in the Lactuceae. All species included in the test were shown to be susceptible to at least one of the isolates. A high incidence of leaf spot or blight resulted from inoculation of most individuals. All plants of six test species were killed after inoculation with one of the isolates of A. cichorii. Several of the test species have not been previously recorded as hosts for A. cichorii. Surprisingly, the known host-range for this fungus is restricted to only few members of the Asteraceae (Acroptilon repens, C. endivia, C. intybus, Carthamus tinctorius and Lactuca sativa). Our results indicate that A. cichorii has a wide host range within the Asteraceae and that other cultivated or non-cultivated members of this family may serve as inoculum reservoirs for this fungus in the absence of cichory, endive or escarole. An attempt to verify if contaminated seeds might be the original source for such geographically distant occurrences of A. cichorii in Brazil was made. Analysis of 24 samples of cichory and endive seeds obtained from dealers in five different Brazilian states showed that 25% of these samples carried A. cichorii with an incidence varying from 0.6% to 13.75%. Such a result highlights the vulnerable situation in Brazil for avoiding introduction of exotic seed-carried vegetable pathogens. It is known that a very significant proportion of vegetable seeds marketed in Brazil are imported and seed inspection for pathogens is not performed regularly for such material imported for commerce. It is probable that contaminated cichory, endive and escarole seeds served as a vehicle for introduction of this fungus in Brazil and that the fungus has then become naturalized in many vegetable growing areas and is now surviving on other Asteraceae in the absence of cultivated hosts.